<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        var a=12;
        //alert(typeof a);//number
         a='abcdg';
         //alert(typeof a);//string
        a=true;
       // alert(typeof a);//boolean

        a=function(){
            alert('abc');
        };
      //  alert(typeof a);//function
        a=document;
       // alert(typeof a);//object

        var b;
        alert(typeof b);//undefined

    </script>
</head>
<body>

</body>
</html>